Booster brake mechanism



Aug. 26, 1958 w. sTELzER BOOSTER BRAKE: MECHANISM Filed June 25, 1954 [kllllilllll IN VEN TOR. W/z /AM 5751.25@

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United States Patent 2,848,877 l BOOSTER BRAKE MECHANISM William Stelzer, Summit, N. l.

Application June 25, 1954, Serial No. 439,331

14 Claims. (Cl. 60-54.6)

This invention relates to a booster brake mechanism, and more particularly to a two-stage master cylinder preferably using the steering booster oil pressure as a source of power.

An important object of the invention is to provide an apparatus which eifectively applies the brakes in the event of a failure in power, which is especially important for booster mechanisms operated by low brake pedals.

A further object is to provide a two-stage brake booster of the type referred to wherein a small piston reacts on the foot pedal during normal operation to provide the pedal with feel and wherein a large piston, serving only in the event of a failure of power, transmits a large volume of lluid to the wheel cylinders to set the brakes.

A further object is to provide in an apparatus of this character a spring cushion in the manually operated connections to eliminate unpleasant feel or lump during the change from the first stage to the second stage of operation while a failure in power exists.

A further object is to provide an apparatus of this character wherein application of the brakes by the pedal in the event of a power failure is not disturbed by the application of power when the hydraulic pump for the steering mechanism becomes operative during the brake application.

Other objects and advantages of the invention will become apparent during the course of the following description.

In the drawing I have shown one embodiment of the invention. In this showing:

Figure l is an axial sectional view through the booster mechanism showing also in section a throttle valve used n conjunction with the apparatus, the wheel cylinders, and the pump, sump and hydraulic steering mechanism associated therewith being diagrammatically illustrated;

Figure 2 is a detail fragmentary sectional view on line 2 2 of Figure 1; and

Figure 3 is a detail axial sectional view through the control valve.

Referring to Figure 1, the numeral designates a master cylinder as a whole comprising a pair of cylinder bodies indicated as a whole by the respective numerals 11 and 12.

The body 11 is provided therein with a cylindrical bore 13, forming one master cylinder space, and a piston 14 is slidable in such cylinder and is provided with a lipped seal 15 which prevents ilow of hydraulic uid from the bore or cylinder 13 to the left past the piston 14, but which permits flow of hydraulic fluid in the opposite direction under conditions to be described. The piston 14 is provided with an axially extending sleeve 16, shouldered as at 17 for engagement with a ring 18 normally engaging a shoulder 19 formed at the left-hand end of the cylinder 13 as viewed in Figure l. The ring 18 is slidable in a larger cylinder 20, coaxial with the cylinder 13. A return spring 21 in the cylinder 13 urges the piston 14 to the o position shown. y

A spring 24 is arranged in the cylinder 20. This Figure l.

spring engages at one end against the ring 18 and at its opposite end against a snap ring 25, and it will be apparent that the spring 24 urges the ring 18 to its off position shown in Figure l when the apparatus is not operating.

The body 12 is provided with a cylindrical bore 28 in which is arranged a piston 29 provided with a lipped seal 34B and dividing the bore 28 to form a pair of chambers 31 and 32. The seal 30 prevents ow of uid past the piston 29 from chamber 32 to chamber 31 but per- 'f mits ow of fluid in the opposite direction.

The piston 29 is provided within the chamber 31 with a sleeve portion 34 in which is slidable a piston 35 carrying a piston rod 36 extending loosely through an opening 37 in the right-hand end of the piston 29 as viewed in A snap ring 38 limits movement of the rod 36 to the left relative to the piston 29, to the off position shown in Figure l.

The rod 36 has its free end slidable in the sleeve portion 16 of the piston 14. A spring 40 has one end engaging the sleeve portion 16 and has its other end engaging a seat 41 backed up by a snap ring 42 carried by the rod 36. The spring 40 accordingly urges the rod 36 to its off position shown. Within the end of the interior of the sleeve portion 16 is arranged a resilient cushion 43 engageable under certain conditions by the rod 36, but

the end of such rod is normally spaced from the cushion 43 as shown in Figure l.

Parallel to the axis of the master cylinder, the body 11 is provided with a bore- 46 in which is arranged a valve indicated as a whole by the numeral 47 and further described below. The body 12, in the face thereof adjacent the body 11, is provided with an annular recess 48 forming a shoulder 49 against which seats one end of the valve 47 when the latter is in its o5 position shown in Figure l. A valve operating lever 51 straddles the rod 36 and has one end looped as at 52 to rock in the bottom of the recess 48 as viewed in Figure l. The upper end of the lever 51 engages in a groove 53 in the valve 47 to impart movement thereto as described below. A coiled spring S4 seats at one end against the piston 29 and at its other end against the lever 51 to tend to hold the latter against the snap ring 42, thus tending normally to hold the lever 5l and valve 47 in their normal off positions.

As will be further noted below, the spring 54is somewhat weaker than the spring 24.

The piston 35 has its inner end tapered to form a valve end 56 normally spaced from but engageable with the adjacent end of the opening 37. To the right of the piston 35, a chamber 57 is formed in the piston sleeve 34 and is in xed communication with the chamber 31 through a port 58. The chamber 31 is in constant cornmunication through a port 59 with a hydraulic uid line 6G, further referred to below.

The left-hand end of the piston sleeve 34 is enlarged as at 64 to slidably receive the enlarged end 65 of the valve 35, and within the sleeve portion 65 is slidable a head 66 having a reduced end 67 slidable in a bore 68 formed in the valve 35. A cushion spring 69 is arranged in this bore to resiliently oppose movement of the head 66 toward the right from its normal o position shown in Figure 1. The head 66 is movable relative to the valve 35 solely against the compression of the spring 69, within the limits of the space at the right-hand side of the head 66. Movement of this head to the left is limited by a snap ring 71.

A push rod 74 is provided with a head '75 extending into a head 66 and preferably engaging the cushion 76 within such head. The push rod 74 is mechanically connected in any suitable manner to the vehicle brake pedal (not shown), and the rod 74 may be considered to be the manually operable element for imparting movement to the-parts ofthe apparatus as further described below,

in order toeiect--application-of the vehiclebrakes.'

The body 11 is provided with a bore 76 transverse to and communicating with the bore 46 as shown in Figmaster cylinder 13 as viewed in Figure l: A sealedpistonm 7 S'is slidable 'in thet boreA `i' 6 "and carries `thereabove i a valve-79engageablefwith a seat VSil-fortified at the' lower end of a bore-S1 lofe'larger 'diameterV` than and-extending above thebore 76. The bore`81is closed at its'upperiend byf-a capZ,l and a spring 33"'is interposedbetween this capiand thevalve-79 to normally hold'thelatterseated as l shown inV Figurel.

The valveseat 80 limits-downward movementof the valve 79 and'piston-78. The space-within thebore 7,6 belowA the piston 78 communicatesthrough a port 34-with a hydraulic uidline S -having,branches'dleading' to the wheel cylinders' ofthelvehicle, two-ofwl'iich-have beenE illustrated andlindicated Aby VtheA numerall 37:

Between the piston '7S and valve 79, a restricted-passage 88"' is drilled' through'thebody 11.* The'other'iend of this passage communicates V withtheerecess 43 throughMv passages 89 in thebody 12. Thebody A11 is provided with a similar restricted passage 90 communicating at one end with the bore'81 and at its'opposite end with va passage 91'v .Y

in the body 12, the latter passage'communicating-with the` port 59. Y

ThefvalveY 4/ 'isrprovided'with a head 94- Figure 3) toward'one 'end-ofthe valvex- Toward its other end, the valve is provided with another relatively'longY head or land 95 iirvvhich the groove 53 is formed. Intermediate these-heads the valve is reduced as at 96, and the lefthand end of the-head 94 accordingly forms a shoulder 97 which, in the normal `ott positions of the parts,is arranged slightly to the left of the left-hand limit of' the' bore376 to disconnectV the Vlower end of-thisbore^from the space around the valve shankY 96. The space around such., shank is indicated in Figure 2 by the'numeral 98, andthis space is in xed communication through'a lateralport99-4 with a fluid line 100, further referred to below.

The valve heads'94 and l95 lare preferably provided with O-rings 101'jand 102, the latter of which seals the valve against leakageY between the Vrecess 48 vand the inner end of the bore 76. TheV O-ring'101'seals against leakage between'the lower endtof the; bore 76'andthe right-handV end of the bore 46 when thek O-ring'101fis moved intoV such bore end under conditions to bedefy cates with the passage 77 when the valve is in the oli posij tion shown in Figure 1. an yaxial passage 108 eXtending'therethrough,-and such passage is always in communication at one end with the The valve 47 is provided with right-hand end of the bore46 and at its other end with the chamber 32.

The present apparatus is particularly intended to utilize the hydraulic system of a power steering mechanismas its source of power. Such a system has been diagrammatically illustrated in Figure l. The system comprises a pump 110 having a discharge line 111 and a return or inlet line 112, the other end of which is connected to a sump 113. In the manner to be described, the pump 110 circulates hydraulic fluid to the power steering mechanism, diagrammatically indicated at 114, through a pipe 115, and a line 116 leads from the mechanism 114 back` to-the sump 113. The line 60 also is connected to the sump as shown, to return hydraulic fluid from the present apparatus to the sump.

A throttle valve mechanism indicated as a whole by the numeral 120 is employedaforA controlling' pressures Vin Y the brake system. The throttle valve mechanism comprises a body 121 having a bore 122 therein in which is slidable a valve element 123 having at one end a valve 124 engageable with a seat 125 opening into a port 126 to which the line 111 is connected. The end of the valve element 123 adjacent the vali/e124; is reduced to provide a space 127 in communcationwith a port 128 to which a pipe 115 is connected.

The va'ive element 123, is provided with a bore 129 in which is arranged a spring 130 engaging a ball valve 131 to tend to'maintain such-lvalveagainst-a seat-'132cmtrolling a passage133 leadingy intorthe. port 126. The valve element 123'is ported as at 134 for the flow of fluid from the passage 133 into the space 127 and into the line 115 when the valve 131 is opened in the manner to be described.

At the right-hand* end oftheA valveI elerne'rit123y a space or chamber 1361s formed in "the i bore 122.,r andA in Vthis'fespace-is arranged a spring 137'sengagingf-thevalve element 123 to normally maintain the valve 124-3seate`di-e Themy space 136fis in tixedrcommunicationwvith a por-t1138ffto which is connected Athevline '-85.7vk The spring'130 engages L n at its'right-handend-against a plugf'139L which formsnin-W eiect a part Yof the' endof'the'rvalve-element-123-so-that thetentire areaof'this'valve element at theright-hand--side thereof is affected by=hy'draulicl pressure in `theL space 136 fs for a purpose to beA described.--

The `body'121A is provided'wvith a lateral-portf142-to l which is connected oneI end 4of the line 100,1 this line lead-fV ing to the port 99 -(-l-TigureLZ) 'as previouslyy statedJ- Comui munication between thejportA 142 andthe passage' '126 Ais controlled bya checkvalve'-143 opening -away lromt-he-l port "126, as -will be obviousz-- Y Operation` The apparatus'deriv'es its powerpreferably'frdnif the hydraulic pressure generated bythe pumpus'ed with `a hydraulic steering mechanism. When the brakeis notl in operation, no pressure will be`presentinthe chamber 136 of the throttle valve'120l Accordingly, the pump 110 circulates fluid through line 111, p ort 126, .pastA valve 124,v which is free to open opposed. only by the tension of the`spring 137,` throughportV 128"and line 115,"'thence through the hydraulic steering mechanism 114 andback to the sump 113 through line 116,- the pump intakeline L 112 supplying hydraulic fluid from the'sump to thei'int'ake side of the pump Y110.v

The` parts of the brake mechanisrn normallyf occupyf the positions shown in Figurel l. Whenthebrake is to/ be operated, the brake'jpegdalffnot shown) is depressed f to move the rod'74 5to the'right. There being no. opposition to movement of the" rod 36 exception thl light spring 40, movement ofthe rod 74`will be transmitted to the rod 36 through spring 69.' This' movement rocks the valvelever 51, about its lower end Y.asviewed `in` Figurel, andthe upper end of the lever moves dthe valve 47 -to'the right'so that theV shoulder 97 move'spa'st the' I` left-hand limit of the bore 76'."

Fluid from the pump 110 willnow flow from port' 126 past check valve 143 Vand intof the line 100, and from this line (Figure 2); hydraulic duid ow's into thespalce 9S around the stem 96'o the'v'alve 475' This Vfluid liows y. into the bore Y-76V beneaththe piston 78,.'thence through port 84 through lines 85 and 86, andthusinto the wheel cylinders 87'." Fluid'also'ows into the chamber'136'of. the throttle valve Vthrough line'SSfand hydraulic pressure in the chamber 136, acting on the adjacentend ofthe valve elementrr123 tends to hold'the valve 124 on"v its seat 12s. rhisrprcvides, through une retrete.,y Suitable pressure foroperatingthe-`brakes, since the valve 124f'has` its opening movement resistantto a substantially`V greaterv j extent than when the brake" mechanism .is not; operating'. 1. However, excessive pressure cannot be built up .in the port 126 of the throttle valve since, at a predetermined pressure, the ball valve 131 will open permitting the flow of uid through port 134 and line 115 to the steering mechanism. Accordingly, ample hydraulic pressure for operatingthe brakes is provided while maintaining an adequate flow of hydraulic uid through the steering mechanism. The brake mechanism does not substantially reduce the iiow of uid through the steering mechanism since the quantity of uid used for operating the brake is not suihcient to affect pressures utilized for operating the steering mechanism.

When the valve 47 is moved in the manner described, the O-ring 11B-1 enters the right-hand end of the bore 46 and seals the space 137 from the lower end of the bore 76. Thus fluid is prevented from flowing from passage 84 into the right-hand end of the bore 46 and thence through the passage 108.

The lower end of the bore 76 (Figure 1) is in constant Communication with the master cylinder 13 through passage 77. Accordingly, whatever pressure is delivered to the wheel cylinders upon operation of the valve 47 will be duplicated in the cylinder 13. Pressure in the chamber 13 acts against the piston 14 to provide the brake pedal with feel except in the initial movement before the brake shoes are in contact with the drums, during which time the spring 24 holds the piston 14 in the position shown in Figure l. A higher pressure in the wheel cylinders, and accordingly in the cylinder 13, causes the piston 14 to move to theleft in Figure 1 to engage the pad 43 with the adjacent end of the rod 36 to transmit reaction forces to the brake pedal proportional to the pressures which are applying the brakes.

The valve 79 opens under conditions to be described. While this Valve is closed, the piston 14 and rod 36 move only a sufficient distance to operate the valve 47. After a predetermined braking pressure is built up, hydraulic pressure beneath the piston 78 moves this piston up- Wardly to open the valve 79 against the tension of the spring 83. The relief valve 131 of the throttle valve prevents a building-up of pressure in the port 126 beyond a predetermined pressure which must be higher than the pressure at which the bypass valve 79 opens. After the spring 83 yields to hydraulic pressure beneath the piston 78, there can be no further increase in fluid pressure in the chamber 13 because of movement of the valve 47. Opening movement of the valve 79, as described, affords communication between the restricted passages 38 and 9@ for the ow of hydraulic liquid from the chamber 32 through the passages S9, 88, 90 and 91 to the port 59 and thence back to the sump 113 through line 6i?.

Further depression of the brake pedal then causes rod 36 to advance, carrying With it the piston 14. This additional movement of the rod 36 closes the valve 56, thus disconnecting chambers 31 and 32 from each other. The seating of 'the valve 56 causes the rod 36 to carry with it the iow pressure piston 29. This movement of the piston 29 displaces fluid from the chamber 32 back to the sump in the manner described. No noticeable reaction changes occur through the brake pedal during this operation, since the brakes have already been set and the reaction ratio through the piston 14 remains the same. No braking forces are generated by :duid from the chamber 32 since, in the normal operation of the apparatus as just described, this chamber is open to the sump for the free flow of uid thereto.

As previously stated, the operation referred to takes place with little movement of the piston 14 and rod 36. However, as the operator continues to exert pressure on the pedal, the piston 14 is advanced to increase pressure in the master cylinder 13 to subject the brake cylinders 87 to increased brake applying pressure. The piston 14 is of relatively small diameter and, accordingly, substantial pressure is generated by foot pressure against the pedal. Thus the operator by foot pressure may generate in the brake cylinders a pressure higher than that which into space 98 (Figure 2), thence through line 10() to seat the ball valve 143 against the lower pump pressure.

When the brakes are to be released, the brake pedal is released by the operators foot and upon retractile movement of the rod 74, fluid from the wheel cylinders ows into the chamber 13 to return the piston 14 to the position shown in Figure 1. Pressure in the wheel cylinders, accordingly, drops to the pressure existing in the chamber 136 of the throttle valve. By a further releasing of the brake pedal, the lever 51 will be returned to the normal position shown in Figure 1, carrying with it the valvev 47 to restore the latter to normal position. This operation opens the chamber 13 to the space 107 around the right-hand endv o f the valve 47 as viewed in Figure 1. rIhis space communicates through notch 106 (Figure 3) with the right-hand end of the bore 46, thence through the aXial passage 108 of the valve to the cylinder 32. With the rod 36 in the off position, the chamber 32 communicates through opening 37, chamber 57, port 5S, chamber 31 and port S9 with the sump 113 through the return line 60. Thus pressure is relieved in the master cylinder 13 and fluid returns to the sump 113. Accordingly, the brakes will be fully released. Of course, the spring 40 will have moved the rod 36 and piston 35 to the 0H position shown, the spring 40 being stronger than and overruling the spring 54.

In the event of a failure of power, as when the pump 110 is not running, actuation of the rod 74 causes the valve 56 to pick up the piston 29 to move it toward the right in Figure l1, the passage through opening 37 thus being closed and fluid being trapped in the cylinder 32. This fluid will be transmitted to the chamber 13 by escaping past the lip of the cup 15, this cup or seal permitting such How of hydraulic uid as previously stated. The piston 29 being of substantially greater area than the piston 14, the manual operation, without power, in the manner referred to displaces a substantial volume of fluid into the chamber 13, thence through line 77, bore 76 and lines 85 and 86 into the brake cylinders to move the brake shoes into engagement with the drums- After the brakes are thus set, pressure in the lower end of the bore 76 moves the piston 78 upwardly, whereupon fiuid can iiow from cylinder 32 through restricted passages S9, 88, and 91 back to the sump 113 through port 59 and line 60. The large volumetric displacement of the piston 29, therefore, is effective for setting the brakes, and after this piston has served its purpose, it is relieved ofthe performance of any further duty. During this operation, the pressure drop between the bore 76, beneath the valve 79, and the passage 90 is gradually decreased because of the increasing pressure acting upwardly on the piston 78. This causes a softening of the pedal or a change in reaction ratio which is satisfactory for the emergency operation being considered. This operation makes the driver aware that the operation is not normal, and under such conditions perfect feel is less important than the effectiveness of the brakes.

If more braking action is then desired, further depression of the brake pedal will move the piston 14 in the chamber 13, thus increasing the pressure in the brake cylinders through passage 77, the lower end of the bore 76 and the lines S5 and '86. Thus the piston 29, in a manual brake application, displaces the relatively large volume of uid necessary to set the brakes, whereupon the substantially smaller piston 14 generates Whatever braking action is necessary.

In order to prevent premature opening of the valve 79 when the brake pedal is depressed violently, passages 88 and 9i) are restricted, thus causing a high resistance to a rapid fluid flow. The spring 69 is preferably of such strength as to yield about when the valve 79 opens. A

suddenv forward movement .of-the rod v36 .occursina fast r brake application,.andpressure,img thefgchamber de- ,e creases due to the-openingqofthe valve Y79, but such decrease `in pressureis `not particularlynoticeable 'to the operator since the spring 9. serves to,maintain a relatively uniform reactionV against ther-brake pedal.Y

In anotherfaspect ofthe. operation andt assuming .that

- the master cylinder` is `in Yits ysecond stage of operation would be communicated to Vtherwheel cylinders'rthe same e as in a normaloperationand the'y chamber ,13.would .be subjected to the same.pressure,VV However-,this would simply vvcausefthe piston 14;tofyieldluntil the Valve 47 shuts olf and* relieves the pressure,V

From the foregoing .it will be apparentfthat the presentv construction is Yparticularlyuseful.for operation by. hydraulic pressure available where power steeringv mechanisms are employed, and that Vthe apparatus `is especially useful in connection with low brake pedals. inV the event e of a failure of power. The -small piston 14.l is effective in normal operation Yto providefthe brake pedal with yac-V curate feel and the larger piston295functions only in the event of a failure of power to transmitV a largevolume of fluid to the wheel cylinders'to set the brakes. spring cushion in the manually operated elements, namely the spring 69, eliminates any-'unpleasant feel or lump during the change fromVr thenrst stage'tothe second stage during a failure of power lfor the apparatus.

It is to be understood thattheform of the invention The' illustrated is Yto be takenY as, a preferred .example of the.

same and that the scope of the invention is dened in they appended claims.k

I claim: l. A booster brakemechanism fora brake system having Vwheel cylinders, comprising a source ofhydraulic pressure, a pair of cylinders ofA different diameters hav-V` ing fluid connection with the wheel cylinders, a small piston in the smaller cylinder anda largetpiston in the larger cylinder, manual .means connectedffor effecting movement of said pistonsto ydisplace hydraulic fluid from said cylinders, a'valve connected to normally cut off communication between. said source andthe wheel cylinders and being connected to bemoved by movement of-said manual means from a normal off position tovconnect said source to the wheel cylinders, said smaller cylinder communicating with the wheel-cylindersatobe subject to pressure therein to `proportionately react against Ysaid manual means, control meansconnected to be responsive to pressure in said source when said valveis operated to .1 return uid from the Vlarger Vcylinder to saidsource Vto render said larger cylinder inoperative when pressure is present in said source, and means connected to be operative when pressure in said larger cylinder is higher than,V pressure in said smaller cylinder to'bypass fluid from theV Y former to the latter upon a failure of power in said 2. yApparatus in accordance with-claim l wherein said smaller piston is constructed to bypass fluid fromv said l the wheel cyhnders and connected to be operative `bythe. v:

pressure of iluid bypassedfrornisaid Alargercylinder to said smaller cylinder upon a failure `of power in said i source,.to releasefluid from said largerwcylinder whenthe bypassed iuid affecting saidcontrol means reaches a predetermined pressure.

3. A booster brakeV mechanism `fora brake system having wheel cylinders, comprising-a source of hydraulic i pressure having a low pressure intake,^a pair of cylinders of diEerent diameters lilledwith hydraulic iiuid, a small pis'tonin the smaller cylinder,.a largeepiston in the larger Y A ai,

cylinder, a rod connectedto bemovahle in onedirection Y to move said pistons .and nrIhally occupying an olf posi? tion -in which it has lo'stmotion `connection` with botliV ik pistons, manuallyroperable means connectedjfor moving@ Y, lsaid rod away from its off position',passage'means Aconi` nestingv the smaller cylinder'tothe-vehicle wheel cylinders, a valve, a lspace in communication-with said source and connected to be controlled by said valve, said valve ,Y

occupying a normal offposition diseonnecting's'aid vspacef` from'vsaid passage means, and connectedjtobe movable v toppen position to conneet'said space tojsid passage; meansrby initial movement of saidrod fromitsnormal off position, whereby, before moving Asaid pistons, said f rodl will kopen said valve, control'means connected to be. Vresponsive to the building up of a predetermined pressure in said passage means for connecting said larger cylinder V- Vpassage means comprises a bore,l said control means comprising a pistoufin such bore subject to pressures therein, anda valvel connected to said piston and con. trolling communication between `said largercylinder and said intake. e e e s 5. Apparatus accordingto claim 3 wherein Vthemeansr for bypassing uid from` said larger, cylinder to said smaller cylinder comprises a lipped seal carriedv by saidY small piston and seating when thepressure in -said smaller cylinder is at least as high-as the pressure in said .larger cylinder, the lip of said seal `contractingyvhen the pres-V A sure in said larger cylinder-is higher than the pressurein said smaller cylinder to bypass fluid from theV former to the latter.- Y

6. A booster brake mechanism for a braking system y having Wheel cylinders, comprising a.hydraulic pump having an outletline and'aninlet line, a sumpconnected to the inlet line,-a pair of alined cylinders of different diameters, a small piston inthe smaller cylinder, a large. piston in the larger cylinder, a bore communicating with said smaller'cylinder, passage means connecting one end, of said bore tothe vehicle wheelcylinders, a Yvalve having a reduced portion forming za space therearound coml municating Ywith `the outletlineof said pump,ssaid valve having a land at one end of said reduced portionnor-V mally occupying a position inwhich it isfconnectedito close communication between said space and said end of` said bore, common operating'meansconnected to be movable from a normal off position toiirst move said valve to open said space to'said end of said bore and then transmit movement to.said.pistons,;jcontrol meansin Vsaid bore connectedto be responsive to a predetermined hydraulic pressureV in said end thereof for connecting said larger cylinder to said sump, and r*meansrconnected'to be operative when the vpressure in said larger cylinder is higher than pressure inlsaid smaller cylinder for bypassing fluid fromthe former V'to the-'latter Itofsupply e' hydraulic iluid pressure to said endof said'-` bore and through said-passage means to -the Vwheelcylinders-to apply the brakes.V

7. Apparatus according: to claim6 wherein the; means for bypassing fluid from said larger cylinder to said` smaller cylinder comprises a lippedseal carriedby said smaller piston andcontractable forthe .ow of iiuid from the larger cylinder to the smaller cylinderwhen pressure in the former is higher than pressure. in .thealatten the` pressure ofthe bypassed. fluid, uponav failure of power in said pump, operating saidcontrol meanswhen suchV liuid reaches said predeterminedpressure to connect'said larger cylinder to said sump, whereupon Ymovement of said small. piston displaces additional uid from j said fas-18,877

smaller cylinder to generate higher pressures in the brake cylinders. Y

8. Apparatus according to claim 6 provided with a check valve in said outlet line closing toward said pump whereby communication between saidend of said bore through the outlet line of said pump is closed when said small piston, moving in said smaller cylinder, generates a hydraulic pressure higher than the outlet pressure of said pump.

9. Apparatus according to claim 6 provided with manual means connected for moving said common operating means, and a cushion spring interposed between and engaging said manual means and said common operating means to cushion hydraulic pressure reactions imparted to said common operating means.

l0. A booster brake mechanism for a brake system having wheel cylinders, comprising a hydraulic vpump having an outlet line and an inlet line, a sump connected to said inlet line, a pair of alined cylinders of different diameters, a small piston in the smaller cylinder, a large piston in the larger cylinder, an operating rod connected for operating said pistons and normally occupying an off position in which it has lost motion connection with said pistons to be moved an appreciable distance from said oif position before imparting movement to said pistons, a manually operable element connected for effecting movement of said rod, a bore having one end communicating with the smaller cylinder, passage means connecting said end of said bore with the wheel cylinders, a slide valve having a reduced portion forming a space communicating with the outlet'line of said pump, said valve having a land adjacent said reduced portion arranged to normally close communication between said space and said end of said bore, a lever engaging said rod end having one end engaging said valve, spring means connected to bias said lever to move said valve to open said space to said end of said bore, stronger spring means engaging said operating rod and normally holding said lever in a position in which said valve is in its normal position, said stronger spring means being overcome by movement of said operating rod whereby said first-named spring means moves said valve to open said space to said end of said bore, means connected to be responsive to predetermined hydraulic pressure in said end of said bore for connecting said larger cylinder to said sump, and means connected for bypassing uid from said larger cylinder to said smaller cylinder when pressure in said larger cylinder exceeds pressure in said smaller cylinder.

11. Apparatus according to claim l() wherein said valve is operable in a valve bore having one end communicating with said end of said rst-named bore when said valve is in normal position and closed to communication therewith when said valve is moved from its normal position, said valve having an axial passage therethrough atording '10` constant communication between said end of said valve Ibore and said larger cylinder for the return ilow o'f uid from said passage means and said smaller cylinder through said axial bore to said larger cylinder when said valve returns to its normal position, and means connected to aord communication between said larger cylinder and said sump when said operating rod is in its ot position.

l2. Apparatus according to claim l0 provided with a check valve in said pump outletline closing toward said pump, such check valve closing when movement of said operating rod causes said small piston to generate'in said smaller cylinder a pressure higher than the outlet pressure of said pump.

13. Apparatus according to claim l0 wherein said valve is operable in a valve bore having one end communicating with said end of said first-named bore when said valve is in normal position and closed to communication therewith when said valve is moved from its normal position, said valve having an axial passage therethrough aording constant communication fbetween said end of said valve bore and said larger cylinder for the return ow of uid from said passage means and said smaller cylinder through said axial bore to said larger cylinder when said valve returns to its normal position, means connected to aiord communication between said larger cylinder and said sump when said operating rod is in its oli position, and a check valve in the outlet line of said pump closing toward said pump and movable to closed position to disconnect said outlet line from said valve space when manual operation of said small piston generates in said smaller cylinder a pressure exceeding the outlet pressure of said pump.

14. Apparatus according to claim 10 provided with a valve bore in which said valve is movable, said valve bore having an end communicating with said end of said rstnamed bore when said valve is in its normal position and being closed to communication therewith when said valve is moved from normal position, said valve being provided with an axial passage therethrough communicating at one end with said end o'f said valve bore and at its opposite end with said larger cylinder, said large piston having a chamber therein communicating with said sump and communicating with said larger cylinder when said operating rod is in its oi position, said operating rod having a valve engaging said larger piston upon predetermined movement of said rod from its off position to close communication between such chamber and said larger cylinder and to impart movement to said large piston.

References Cited in the le of this patent UNITED STATES PATENTS 

